Insulation coating and method of application thereof



March 13, 1962 E, P, LARSH T AL 3,025,188

INSULATION COATING AND METHOD OF APPLICATION THEREOF Filed Aug. 26, 1959INVENTORS EVERETT P. LARSH 8 BY FRANKLIN E. COPPOCK ATTORNEY tritefitats This invention relates to insulation coating material and to themethod of application thereof. The invention relates more particularlyto a ceramic electrical insulating coating for surfaces of portions ofelectrical machines. The invention relates still more particularly to acoating for the slots of rotors and stators of electric motors. Howeverthe invention i not so limited in that it may be used for coating ofother surfaces.

An object of this invention is to provide an electrical insulationcoating material for the surfaces of portions of elements of electricalmachines, such as a coating for the wall surfaces of the slots of rotorsand stators.

Another object of this invention is to provide such a coating which canbe easily and readily applied at cornparatively low cost.

Another object of the invention is to provide such a coating which isextremely durable and has long life.

Another object of this invention is to provide such a coating which hasvery fine electrical insulation properties, which is capable ofwithstanding high temperatures, and which is not subject todeterioration by moisture.

Another object of this invention is to provide such a coating which maybe applied and used in a very thin form. Thus, the coating does notappreciably interfere with heat conduction from a winding.

Another object of this invention is to provide a coating material andmethod of application thereof which cleans a surface as it is appliedthereto so that a separate cleaning process is not required.

Another object of this invention is to provide a coating for the slotsof a laminated rotor or stator which coating when applied makes possiblethe insertion of conductor material into the slots without interferencewith the relative positions of the laminations; thus treatment of thelaminations after application of winding material is eliminated.

Another object of this invention is to provide a coating process inwhich a portion of the process can be carried out simultaneously with aheat treating process for normalizing or annealing of the steel of thelaminations.

The material and process of this application may be used in connectionwith the provision of an electrical insulation coating to the surfacesof portions of elements of electrical machines. The invention isprimarily adapted to the provision of an electrical insulation coatingto the surfaces of slots of a stator or rotor of an electric motor.

The coating of this invention may be applied to the slots of rotors andstators in the manner shown in copending application Serial No. 690,705,filed October 17, 1957, in which two of the inventors therein are alsothe inventors in regard to this application. Said application disclosesthe method of passing a slurry through the slots of an element, such asa rotor or stator, of an electric machine.

The FIGURE in the drawing illustrates apparatus which may be used toapply a coating of this invention.

A coating chamber is shown containing an electrical element such as anannular stator member 12 which has a plurality of slots 14 at the innerportion thereof. The apparatus is adapted to coat the surfaces of theslots 14. The member 12 may also be a rotor or other element havingportions for coating in accordance with this in- Patented Mar. 13, 1962ice vention. Suitable sealing members such as 16 and 18 engage the outeredges of the stator 12. An elastomeric mandrel 20 is adapted to havepressure applied therein by means of fluid from a conduit 22. which isforced into the mandrel 20 and urges the mandrel Z-il into firmengagement with the inner surfaces of the stator 12. Conduit members 26and 28 are connected to the coating chamber 10. Thus, only the slots 14are open as passages for flow of fluid through the chamber 111.

The conduit members 26 and 28 are also connected to any suitablefour-way valve member such as the rotary valve 30. A fluid line 34extends from the valve member 36 to any suitable pump device 36 whichpumps fluid from a tank 38 to the four-way valve 34 The tank 38 containsa quantity of the coating composition discussed below. If desired, thecoating composition may be agitated by means of an agitator member 40. Areturn line 42 connects the valve 30 to the tank 38.

Preferably, a suitable vacuum pump 16 is connected by a line 48 to theconduit 28 for evacuation of the coating chamber 10.

v stator 12 by means of any suitable fluid forced into the mandrel 20through the conduit 22. Then, the pump 36 is started and circulates thecoating composition from the tank 38 through the valve and through thelines 26 and 23.

By suitable operation of the valve 311 the coating solution from thetank 33 can be forced through the slots 14 of the stator 12 in onedirection, followed by forcing the solution from the tank 3 8 throughthe slots 14 of the stator 12 in the opposite direction. After thedesired period for such circulation of the coating composition, the pump36 is stopped and the vacuum pump 46 is started for evacuation of thecoating chamber lit to draw all excess fluid from the slots 14 of thestator 12 and from within the coating chamber 1%. Then, a vent valve 59connected to the conduit 28 is opened, permitting restoration ofatmospheric pressure to the coating chamber 16*. Then, internal pressureis removed from the mandrel 20 by removal of the fluid pressure which isapplied through the conduit 22. The coating chamber 10 is then openedand the stator 12 is removed.

The coating of this invention comprises ceramic material of finelydivided particles which are carried in a suitable liquid vehicle to forma slurry. The slurry is passed through the slots of the element of theelectric machine. Some of the finely divided particles are depositedupon the wall surfaces of the slot so that when passage of the slurry isstopped the finely divided particles remain upon the Wall surfaces ofthe slots. The vehicle which carries the finely divided particles is onewhich readily evaporates when the electric machine element is exposed toroom temperature following passage of the slurry through the slotsthereof.

Then the element of the electric machine is placed in an oven or thelike in which the temperature is brought to a value slightly above thefusing point of at least some of the finely divided particles. Thus, theparticles are joined and firmly bonded as a coating upon the surfaces ofthe slots.

The slots are ordinarily formed in the slots of punched laminations, thelaminations having edge portions thereof which are somewhat hardened bythe punching process. It is customary to anneal or normalize the steelof the laminations after the punching process in order that the steel ofthe laminations will have its best magnetic qualities. The process ofannealing can be carried out during and immediately following the fusingof the finely divided particles in the forming of the coating upon thesurfaces of the slots. Preferably, the finely divided material isselected so that a portion thereof fuses at a temperature which is alsoa favorable temperature for heat treatment of the steel of thelaminations. Thus, the fusing and heat treating are carried onsimultaneously. The fusing process requires a lesser amount of time thanthe heat treatment process, but after the desired temperature isobtained in the electrical element for the fusing and for the annealing,the temperature may be maintained for a somewhat longer period after thefusing occurs in order to complete the heat treatment process. However,the heat treatment temperature employed may be slightly lower than thefusing temperature of the frit so that the temperature may be reducedslightly after the fusing and during the heat treatment of the steel.

In this invention, in general, a suitable composition for passing overthe surface to be coated is as follows:

50 to 75 parts, 150 to 250 mesh frit of fusion point from 800 to 1200 F.15 to 35 parts, 75 mesh to 150 mesh frit of fusion point 1400 to 1600 F.1 to 10 parts silica, finely ground 1 to 10 parts tabular alumina 1 to10 parts asbestine, finely ground 3 to parts of a liquid vehiclecomprising:

3 to 15 parts acetone 0 to 5 parts lower of a lower alkyl acetate 0 to 5parts alcohol-- In which all parts are by weight A composition such asset forth above is forced to flow over a surface to be coated. Forexample the composition may be forced through the slots of an element ofan electrical device such as a rotor or stator upon which it is desiredto place an insulation coating prior to providing a winding within theslots. Such a process is disclosed in our said copending applicationSerial No. 690,705. The finely divided particles are deposited upon edgeportions of the laminations in which the slots are formed. Aftersufficient flow of the composition to deposit the desired amount of thefinely divided particles, the flow of the composition is stopped and anyportions of the liquid vehicle which remain in the slots or upon thesurfaces are permitted to evaporate.

The element is then placed into a furnace or the like in which thetemperature of the element is brought to a value slightly above the fusepoint of some of the finely divided particles. For example, in the useof the composition set forth in the above example, the frit having thelower fusing temperature fuses readily at 1200 degrees Fahrenheit. Afterthe deposition of the finely divided particles upon the surface to becoated, the element having said surface is brought to a temperature ofabout 1200 to 1250 degrees Fahrenheit. Thus, the lower fusing frit fuseswhile the second frit of higher fusing temperatures does not fuse. Thefusing of the first frit requires only a few minutes.

However, due to the fact that a temperature of 1200 to 1250 degreesFahrenheit is a very suitable temperature for heat treatment of steelsused in the laminations of electrical elements, such temperature ismaintained for a longer period than is necessary for the fusing of thefirst frit. The longer period of time at this temperature serves to heattreat the steel of which the laminations are composed. The time providedfor the heat treatment is usually not suflicient for a complete heattreatment but is sufficient to treat the steel to a certain economicaldegree. Thus, fusing and heat treating may be carried on simultaneouslyby means of the method of this invention. If annealing is not desired orif heat treatment is to be done at another temperature, a material infrit form may be selected which fuses at a temperature other than 1200degrees Fahrenheit.

After the element is removed from the furnace or the like, the elementis permitted to cool rather slowly for the purpose of completing theannealing or normalizing for maintaining good magnetic steel structurein the laminations.

Thus, the surface to be coated has a good ceramic coating and the steelstructure of the laminations is prepared to a practical economicalvalue.

If it is desired to provide coating having some roughnesscharacteristics, the amount of frit which does not fuse at the furnaceor oven temperature may be greater.

If a rather thin coating is desired, the amount of liquid vehicle in thecomposition may be increased, while a thicker coating may be obtained bydecreasing the percentage of liquid vehicle in the composition. Ofcourse, the thickness of the coating obtained is also dependent upon thelength of time that the composition is forced to flow over the surfaceto be coated.

In some instances the composition is forced in one direction over htesurface for a given time, followed by reversal of the direction of flowfor a given time, as shown in the drawing. It has been found that suchreversal of flow may sometimes provide a thicker coating or a coatingwhich has fewer depressions or pin holes therein.

The alumina, the asbestos or asbestine, and the silica assist inproviding certain refinements in the quality of the coating obtained.Such ingredients may reduce the amount of shrinkage, or may aid in theholding of firmness in the fused coating during the increased time forannealing or normalizing. Such ingredients may also aid in obtaining athicker coating upon a single application thereof or during a shortertime of flow of the composition over the surface.

The coating and process of this invention are particularly adapted tothe production of elements at a high rate such as by automaticallyoperating machines and the like as the elements are operated upon inseriatim relation.

The following examples illustrate more specific embodiments of thecoating compositions of the present invention, but the invention is notto be considered as limited thereto.

Example 1 65 parts frit #801 (1200 F. fuse point) 25 parts frit #2501(1500 F. fuse point) 2 parts silica 2 parts tabular alumina 5 partsacetone All parts being by weight The formulation of Example 1 can bevaried, for example, by adding 2 parts asbestine to aid in holding thewet film in place. The composition may also be varied by utilizing 1 or2 parts of butyl acetate along with the 1ageltone to slightly change thecharacteristics of the ve- Example 2 Parts by 0 weight 200 mesh frit of1200 F. fuse point mesh frit of 1500 F. fuse point 25 Silica powder(coarse) 2 Tabular alumina 2 5 Acetone 5 Example 4 Parts by weight 200mesh 1200 F. frit 60 100 mesh 1500 F. frit 18 200 mesh 1500 F. frit #10silica 2 Asbetine 2 Tabular alumina 2 Butyl ace 6 While the coatingcompositions will ordinarily contain only the described components, itwill be understood that compositions consisting essentially of thedescribed components can be employed even though they may contain minoramounts of other components, such as antioxidants, stabilizers, fillers,or other conventional additives, so long as the added components do notdeleteriously affect the properties of or change the fundamentalcharacter of the coating material.

The coating material, for example that of Example 2, is ordinarilyapplied by flowing over the surface of the machine part for a sufiicienttime to give a coating about 0.001 to 0.002 inch thick, or any otherdesired thickness, and the coating is then permitted to dry with evaporation of the liquid vehicle, and then the part is heated to the fusionpoint of at least the lower fusing frit to fuse the material, and theheating can be continued if desired to anneal or normalize the metal ofthe part. It is preferable to apply the coating under pressure in aclosed chamber, and use forced air drying followed by evacuation of thechamber to set the coating material.

The ingredients and proportions of the coating compositions describedherein can be varied to some extent in certain particulars Withoutdeparting from the invention, as will be recognized by those skilled inthe art in View of the present disclosure.

The ceramic or porcelain enamel used in the invention is of a type knownas frit, i.e., an enamel such as a complex alkaline boro-silicate glass,usually containing fluorine, produced by melting a mixture such asborax, feldspar, quartz and cryolite. For a lower melting frit, thepresent invention can utilize an enamel of a type in common use andprepared from the above components in portions to give a fusing range inthe order of 800 to 1200 F. Similarly, frits identified by a fusingrange of the order of 1400 to 1600 F. can be selected from those incommon use and prepared from the above components and will be suitablefor the higher melting frit in the composition of the present invention.

The particle size of the frit can also be varied, for example from 300mesh to 50 mesh; it is often desirable to employ two different particlesizes of the higher fusing frit, for example a combination of 200 meshwith 100 mesh; uses of the larger particle size gives added roughness tothe resulting coating. Mesh size, as used herein, refers to particles ofa size to pass through mesh of the designated number of openings perinch, as determined by conventional procedure.

The frits utilized herein, while defined by their fusing temperature,were selected to have and do have the required dielectric strength,adhesion characteristics, minimum shrinkage, flexibility and shockresistance; the frits also have long life at high temperature, asrequired when the fusing process is combined with a normalizing orannealing process for the steel components, for example, two hours athigh temperature.

The silica for use herein is any ordinary, finely divided silica, suchas silica flour; the silica adds roughness and helps retard shrink. Thealumina for use herein is preferably tabular. The alumina is a fillerhaving good electrical insulating properties and helps retard shrinkage.Asbestine, which optionally can be used, is preferably finely dividedfibrous asbestos.

As the liquid vehicle for use in the present invention,

fairly volatile organic solvents are generally satisfactory,particularly those singly or in admixture to provide a. vehicle boilingin the range of about 50 to 100 F., or more preferably in the range of70 to F. A low boiling temperature is necessary to have a quick settingsolution, and to avoid runs in the surface, but if the vehicle boils attoo low a temperature, the application conditions are more difficult tocontrol. Such vehicles can be comprised of hydrocarbons, for example,aliphatic hydrocarbons such as the lower liquid alkanes, e.g., pentane,hexane, etc.; or aromatic hydrocarbons, e.g., benzene, toluol, mineralspirits, etc. However, it is often desirable to use liquids having somepolar properties, or functional groups, e.g., alcohols, ketones, loweralkyl esters, etc. in order to have improved solvent and cleaningproperties along with aflinity for moisture. It is understood that theforegoing or other solvents of the type contemplated Will be utilized inadmixture with each other as and if required to give vehicles of thedesired boiling ranges.

The amount of liquid vehicle for use in coating compositions accordingto the present invention will generally be about 3 to 15 parts by weightper parts by weight of coating composition. However, somewhat largeramounts of vehicle can be used if a thin coating is desired, asordinarily the use of thinner compositions results in thinner coatings.The thickness of a composition suitable for coating purposes accordingto the present invention can also be defined by viscosity or specificgravity measurements. In general, suitable compositions will havespecific gravity in the range of 35 Baum to 60 Baum, the compositionsfor coating the slots of a rotor preferably being in the range of 40 to45 Baum, and those for coating the slots of a stator preferably being inthe range of 50 to 55 Baum to give a slightly thicker coating.

It will be understood that acetone has been found especially suitableand superior as a vehicle in the coating process of the presentinvention because of its combination of proper volatility, solvent andcleaning ability, afiinity for oil and moisture, and because of thedesirable properties of the resulting coating. Examples of other liquidswhich can satisfactorily be employed in the liquid vehicles are butylacetate, methyl ethyl ketone, acetone 80% combined with 20% methylalcohol, toluol, mineral spirits, isopropyl alcohol, methyl alcohol,ethyl alcohol, etc.

While illustrative examples of the compositions and various Ways ofpracticing the process of the present invention are given herein it willbe understood that various changes and modifications can be made withinthe spirit of the invention.

Having thus described our invention, We claim:

1. An insulating coating composition comprising 50 to 75 parts of to 250mesh frit of fusion point of about 800 to 1200 F., 15 to 35 parts of 75to 150 mesh frit of fusion point 1400 to 1600 F., 1 to 10 parts silica,and 1 to 10 parts tabular alumina, all parts being by weight, suspendedin an organic liquid vehicle of boiling point in the range of 50 to 100F. and present in an amount to give a specific gravity of 35 to 60 Baum.

2. The composition of claim 1 in which the liquid vehicle comprisesalcohol.

3. The composition of claim 1 in which the liquid vehicle comprisesacetone.

4. They composition of claim 1 in which the liquid vehicle comprises alower alkyl acetate.

5. An insulating coating composition comprising 50 to 75 parts of 150 to250 mesh frit of fusion point of about 800 to 1200 F., 15 to 35 parts of75 to 150 mesh frit of fusion point 1400 to 1600 F., 1 to 10 partssilica, 1 to 10 parts tabular alumina, 3 to 15 parts of acetone, up to 5parts of a lower alkyl acetate, and up to5 parts alcohol, all partsbeing by weight.

6. An insulating coating composition comprising 65 parts of frit ofabout 1200 F. fuse point and about 200 mesh size, 25 parts of frit ofabout 1500 F. fuse point and about 100 mesh particle size, 2 partssilica powder, 2 parts tabular alumina, and parts acetone, all partsbeing by weight.

7. The method of providing an insulating coating to surfaces of portionsof elements of electrical machines which comprises flowing over thesurfaces a slurry of specific gravity in the range of 35 to 60 Baum andcomprised of S0 to 75 parts of a lower fusing 150 to 250 mesh frit offusion point of about 800 to 1200 R, 15 to 35 parts of a higher fusing75 to 150 mesh frit of fusion point 1400 to 1600 F., 1 to parts silica,1 to 10 parts tabular alumina, all parts being by weight, suspended inan organic liquid vehicle of boiling point in the range 50 to 100 F,followed by stopping the flow of the slurry and permitting the vehicleto evaporate, followed by heating the portion of the electrical machineto a temperature at least as high as the fusion point of the lowerfusing frit to cause fusion thereof, without heating to a temperature toeffect fusion of the higher fusing frit.

8. The method of claim 7 in which the element being coated is in aclosed chamber and the slurry is caused to fiow under pressure over thesurface followed by circulation of dry air through the chamber, followedby evacuation of the chamber to seat the coating in place prior to theheating step.

9. The method of claim 7 in which the machine surface being coated isheated at a temperature at least as high as the fusing point of thelower fusing frit for at least an hour to anneal the metal thereof.

10. The method of claim 7 in which the slurry comprises 65 parts frit ofabout 1200 F. fuse point and about 200 mesh size, 25 parts of frit ofabout 1500 F. fuse point and about 100 mesh particle size, 2 partssilica powder, 2 parts tabular alumina, and 5 parts acetone, all partsbeing by weight.

11. The process of insulating the winding slots of an element of anelectrical machine in which the element is composed of stacked punchingsof sheets of steel material, the method also annealing portions of thepunchings which have become hardened by the punching process, comprisingflowing through the slots a slurry of specific gravity in the range of35 to 60 Baum and comprised of 50 to 75 parts of a lower fusing frithaving a mesh 150 to 250 and a fusion point of about 1100 to 1250 F., to35 parts of a higher fusing 100 to 150 mesh frit of fusion point 1400 to1600 F., all parts by weight, suspended in an organic liquid vehiclehaving a boiling point in the range of 70 to 100 F., followed bystopping the flow of the slurry and permitting the vehicle to evaporate,followed by heating the element to a temperature sufiicient to fuse thelower fusing frit but to a temperature less than that required to fusethe higher fusing frit, followed by maintaining the temperature at sucha value for a period of from one to two hours.

12. The process of insulating the winding slots of an element of anelectrical machine in which the element is composed of stacked punchingsof sheets of steel material, the method also annealing portions of thepunchings which have become hardened by the punching process, comprisingflowing through the slots a slurry of specific gravity in the range of35 to Baum and comprised of 50 to 75 parts of a lower fusing frit havinga mesh 150 to 250 and a fusion point of about 1l00 to 1250 F., 15 to 35parts of a higher fusing 100 to 150 mesh frit of fusion point 1400 to1600 15., all parts by weight, suspended in an organic liquid vehiclehaving a boiling point in the range of to 100 F., followed by stoppingflow of the slurry and permitting the vehicle to evaporate, followed byheating the element to a temperature sufficient to fuse only the lowerfusing frit, followed by maintaining the temperature at a value of about1200 F. for a period of one to two hours.

13. An insulating coating composition comprising 50 to parts of 150 to250 mesh frit of fusion point of about 800 to 1200 F., 15 to 35 parts of75 to 150 mesh frit of fusion point 1400 to 1600 F., all parts being byweight, suspended in an organic liquid vehicle of boiling point in therange of 50 to F. and present in an amount to give a specific gravity of35 to 60 Baum.

14. An insulating coating composition comprising 50 to 75 parts of to250 mesh frit of fusion point of about 800 to 1200 F., 15 to 35 parts offrit of fusion point 1400 to 1600 F. of which up to 50% is about 200mesh and the balance 75 to 15 mesh, 1 to 10 parts silica, and 1 to 10parts tabular alumina, all parts being by weight, suspended in anorganic liquid vehicle of boiling point in the range of 50 to 100 F. andpresent in an amount to give a specific gravity of 35 to 60 Baum.

15. An insulating coating composition comprising solid particles of 65parts of frit of about 1200 F. fuse point and about 200 mesh size, 25parts of frit of about 1500 F. fuse point and about 100 mesh particlesize, 2 parts silica powder, 2 parts tabular alumina, said solidparticles being suspended in an organic liquid vehicle of a boilingpoint of 50 to 100 F. in an amount to give a specific gravity of 35 to60 Baum.

References Cited in the file of this patent UNITED STATES PATENTS2,321,763 McIntyre June 15, 1943 2,391,468 Long Dec. 25, 1945 2,757,105Terry July 31, 1956 2,781,636 Brandes et al. Feb. 19, 1957 2,827,393Kadisch Mar. 18, 1958 2,858,235 Rex Oct. 28, 1958 2,930,713 Hoffman Mar.29, 1960 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION PatentN00 3,025, 188 March 13 1962 Everett P. Larsh et a1.

It is hereby certified that error appears in the above numbered patentrequiring correction and that the said Letters Patent should read ascorrected below.

Column 8 line 32, for "15" read 150 Signed and sealed this 26th day ofJune 1962.

(SEAL) Attest:

DAVID L. LADD ERNEST W. SWIDER Attesting Officer Commissioner of Patent

7. THE METHOD OF PROVIDING AN INSULATING COATING TO SURFACES OF PORTIONSOF ELEMENTS OF ELECTRICAL MACHINES WHICH COMPRISES FLOWING OVER THESURFACES A SLURRY OF SPECIFIC GRAVITY IN THE RANGE OF 35* TO 60* BAUMEAND COMPRISED OF 50 TO 75 PARTS OF A LOWER FUSING 150 TO 250 MESH FRITOF FUSION POINT OF ABOUT 800* TO 1200* F., 15 TO 35 PARTS OF A HIGHERFUSING 75 TO 150 MESH FRIT OF FUSION POINT 1400* TO 1600* F., 1 TO 10PARTS SILICA, 1 TO 10 PARTS TABULAR ALUMINA, ALL PARTS BEING BY WEIGHT,SUSPENDED IN AN ORGANIC LIQUID VEHICLE OF BOILING POINT IN THE RANGE 50*TO 100* F., FOLLOWED BY STOPPING THE FLOW OF THE SLURRY AND PERMITTINGTHE VEHICLE TO EVAPORATE, FOLLOWED BY HEATING THE PORTION OF THEELECTRICAL MACHINE TO A TEMPERATURE AT LEAST AS HIGH AS THE FUSION POINTOF THE LOWER FUSING FRIT TO CAUSE FUSION THEREOF, WITHOUT HEATING TO ATEMPERATURE TO EFFECT FUSION OF THE HIGHER FUSING FRIT.